When opening a stored display or MXD file, the geometric network is not available in the Utility Network Analyst toolbar.
This issue may be related to the following esri bugs.
NIM086307: When a broken (data source)layer other than any of the geometric network layers is in a group layer, the utility network analyst toolbar greys out.
NIM086347: When a broken (data source) layer other than any of the geometric network layers is in a group layer, the Utility Network Analyst toolbar greys out.
This problem may occur if the first layer of a group has a broken data link.
Remove the broken layer from the group, or repair the broken data link.
Visit the ArcGIS Resource Center for information on repairing or removing broken links in a map.